This invention relates to cable manufacture and in particular but not exclusively to the manufacture of quads of electrical conductors for telecommunications cables.
High quality quads of electrical conductors, that is quads with good cross-talk levels, for example, of the order of 70 dB at 1 KHz, are conventionally manufactured by a multi-stage, and therefore expensive, process. There may be up to ten different operations required to manufacture a quad by the conventionally employed method. Basically the conventional method comprises manufacture of a central insulating string; manufacture of conductor wire; manufacture of four separate insulated wires from the conductor wire; rewind and water test the insulated wires for insulation defects; formation of a quad sub-assembly from the insulated wires by stranding them about or laying them up with the central string; and sheathing of the quad sub-assembly with extruded plastics material.
British Patent specification No. 783,064 describes a method of making a quad by heating the conductors and partially forcing them in a matrix (like a die) into a central core of foamed polyethylene in a manufacturing operation. The process is said to be controlled in such manner that, when the core and conductors leave the matrix, the temporarily softened material of the core has already solidified again, so that the conductors are fixed relative to one another, both in the radial and the circumferential direction of the core, in an arrangement which is solely determined by the position of grooves in the matrix.
We believe this cable has never been successfully made. We have found that the application of heat to soften a core as described results in a product which cannot be produced quickly and which does not have accurately spaced conductors to achieve acceptable cross-talk levels.